Modular tulip assembly

ABSTRACT

A modular tulip assembly has a rod receiving tulip and a saddle. The saddle is interlockingly held inside a distal portion of the tulip. The saddle has a locking projection. The tulip has a pair of grooves or recesses. The locking projection is positioned into the proximal tulip groove or recess and holds the saddle in a pre-loaded unlocked state ready to be pushed onto a head of an implanted bone screw. Upon receiving the head of the bone screw, the saddle can be moved distally relative to the tulip to a locked state by moving the locking projection distally into the distal tulip locking groove or recess.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/609,127 filed on May 31, 2017, which is a continuation in part ofU.S. application Ser. No. 15/284,929 filed on Oct. 4, 2016, which arehereby incorporated by reference herein in their entireties.

TECHNICAL FIELD

The present invention relates to an improved modular head tulipassembly.

BACKGROUND OF THE INVENTION

Bone anchor screws come in a variety of shapes and sizes. One of themore common styles has a polyaxial head that allows for the screw toenter the bone structure at an ideal or preferred inclination. Toachieve this polyaxial inclination, the head has a shape configured toallow a complimentary implant device being held by the screw to rotateabout its lower external surface. This lower surface can be one of anumber of shapes like conical or spherical or hemispherical. Thisability is often used in rod receiving implant devices having a modularhead assembly.

The modular head pedicle screw assembly generally includes a tulip. Atulip is a body structure having two opposing sides spaced by a slottedopening to receive a spinal rod. The tulip often employs internalthreads to receive a rod locking set screw to anchor or fix the rod inthe tulip. The lower portion of the tulip has an opening to receive thepedicle screw in a base seat. Often, the tulip can have a saddle thatalso supports the rod along an underside of the rod. The saddle havingan upper recessed curvature into which the rod sits and a lower cup likeopening to receive the top of the pedicle screw head. When the saddleand rod and set screw are tightened, the screw angle is fixed againstthe tulip seat.

Often, it is preferred that the pedicle screw is first placed securelyin the bone structure leaving the head protruding above the bonesurface. In this surgical procedure the tulip assembly must be adaptedto fit down onto the projecting screw head. To accomplish this, thesurgeon must push the tulip onto and over the screw head without a clearpath of vision. Accordingly, the placement must be accomplished withoutany way of knowing if the tulip or other device is properly secured.Thereafter, the device is tightened to complete the assembly and theonly way to insure the assembly is secure requires an upward pulling ofthe tightened assembly. This is not a good test because the assembly maybe loosened or the screw to bone interface weakened.

It is, therefore, an objective of the present invention to provide a wayfor a surgeon to place a tulip assembly onto a pedicle screw alreadythreaded into bone in such a way the surgeon can make a proper andsecure connection easily.

It is a further objective that the device has properly fitted the tulipassembly onto the pedicle screw head by the very nature of the design.It is another objective that the device provides a self-locking featurethat when tightened by assembly, the surgeon can lock the assemblyengagement insuring he has made a proper assembly. These and otherobjectives are achieved by the invention as described hereinafter.

SUMMARY OF THE INVENTION

A modular tulip assembly has a rod receiving tulip and a saddle. Thesaddle is interlockingly held inside a distal portion of the tulip. Thesaddle has a locking projection. The tulip has a pair of grooves orrecesses, a first proximal groove or recess and a second or distallocking groove or recess. The locking projection is positioned into thetulip proximal groove or recess and holds the saddle in a pre-loadedunlocked state ready to be pushed onto a head of an implanted bonescrew. Upon receiving the head of the bone screw, the saddle can bemoved distally relative to the tulip to a locked state by moving thelocking projection distally into the distal locking groove or recess towhere the proximal end of the saddle is past abutting the lockingprojection.

The tulip has a pair of opposing internally threaded walls defining aslotted opening for receiving a rod, an open bore with an open distalend for passing the polyaxial head of the bone screw, and the tulipgrooves or recesses are axially spaced below the internal threads of theopposing walls and above the open distal end.

The saddle has an axis defined by a center opening. The saddle has aproximal end with a concavity for holding a rod and a distal portionwith a plurality of arcuate fingers spaced by slots. The plurality ofarcuate fingers are curved to form at least a hemispherical shapedconcavity for receiving and holding the head of the bone screw. Thefingers extend to a distal end. The saddle has the locking projectionpositioned between the proximal end and above the arcuate fingers. Thesaddle is sized to pass through the open distal end of the tulip andmove axially inside the tulip below the internal threads. The tulip hasan enlarged internal chamber to accommodate the arcuate fingers andsized to allow the fingers to flex outwardly over and past a maximumdiameter of the screw head on attachment.

In one embodiment, the saddle center opening at the proximal end hasinternal threads to engage threads of an end of a tool configured toaxially move the saddle relative to the tulip. The saddle ispre-positioned in an unlocked bone screw receiving state when thelocking projection is moved onto the proximal tulip groove or recess andafter being attached onto an implanted bone screw polyaxialhemispherical head, the saddle is configured to be moved relative to thetulip by rotation of the tool to the locked state by moving the lockingprojection distally from the proximal tulip groove or recess and havingthe proximal end of the saddle moved distally past moving the lockingprojection into the distal tulip locking groove or recess causing thearcuate fingers at the distal end to flex and be compressed at the opendistal end of the tulip. The locked saddle can be repositioned to theunlocked state by attaching the threaded end of the tool to the saddleand rotating the tool as it abuts a proximal end of the tulip causingthe locking projection to disengage the distal tulip locking groove orrecess and move to the proximal tulip groove or recess allowing thearcuate fingers to release the screw head and the tulip assembly to beremoved from the bone screw.

In a preferred embodiment, a modular tulip assembly is configured toreceive and lock onto an implanted bone screw having a threaded shankand a hemispherical polyaxial head. The tulip subassembly has a tulipand a saddle. The tulip has a pair of opposing internally threaded wallsdefining a slotted opening for receiving a rod, an open bore with anopen distal end for passing the polyaxial head of the bone screw, and apair of locking grooves or recesses being axially spaced below theinternal threads of the opposing wall and above the open distal end. Thesaddle has an axis defined by a center opening. The saddle has aproximal end with a concavity for holding the rod and a distal portionwith a plurality of arcuate fingers spaced by slots. The plurality offingers are curved to form at least a hemispherical shaped concavity forreceiving and holding the head of the bone screw. The fingers extend toa distal end, the saddle has an locking projection positioned betweenthe proximal end and above the arcuate fingers. The saddle is sized topass through the open distal end and move axially inside the tulip belowthe internal threads. When assembled to the tulip, the saddle ispre-positioned in an unlocked bone screw receiving state when thelocking projection is moved onto the proximal tulip groove or recess.Thereafter, the saddle in the unlocked state can be attached onto animplanted bone screw polyaxial hemispherical head. The saddle isconfigured to be moved to a second locked state by moving the lockingprojection distally off the proximal tulip groove or recess and havingthe proximal end of the saddle moved distally into the distal tuliplocking groove or recess causing the arcuate fingers at the distal endof the tulip to flex and be compressed at the open distal end of thetulip.

In this preferred embodiment, the tulip has an enlarged internal chamberto accommodate the arcuate fingers and sized to allow the fingers toflex outwardly over and past a maximum diameter of the screw head onattachment. The saddle center opening at the proximal end has internalthreads to engage threads of an end of a tool configured to axially movethe saddle relative to the tulip. The modular tulip assembly has thesaddle pre-positioned in an unlocked bone screw receiving state when thelocking projection is moved onto the proximal tulip groove or recess andafter being attached onto an implanted bone screw polyaxialhemispherical head, the saddle is configured to be moved relative to thetulip by rotation of the tool to the locked state by moving the lockingprojection distally off the proximal tulip groove or recess and havingthe proximal end of the saddle moved distally past and into the distaltulip locking groove or recess causing the arcuate fingers at the distalend to flex and be compressed at the distal end of the tulip. Themodular tulip assembly allows the locked saddle to be repositioned tothe unlocked state by attaching the threaded end of the tool to thesaddle and rotating the tool as it abuts a proximal end of the tulipcausing the locking projection to disengage the distal tulip lockinggroove or recess and move onto the proximal tulip groove or recessallowing the arcuate fingers to release the screw head allowing thetulip assembly to be removed from the bone screw.

A method of assembling a modular tulip has the step of providing a tulipwith a distal and a proximal groove or recess; and positioning a saddlewith a proximal locking projection inside the tulip past the distallocking groove or recess and into the proximal groove or recess insidethe tulip in a pre-loaded unlocked state to receive a head of a bonescrew. The method further has the step of pushing the tulip with thepre-loaded unlocked saddle onto an implanted bone screw previouslythreaded into bone and moving the saddle to a locked state by moving thelocking projection distally off the proximal tulip groove or recess andthe proximal end distally abuts the distal tulip locking groove orrecess. The step of moving the saddle to a locked position furtherincludes engaging internal threads of the saddle with a threaded end ofa tool, rotating the tool to move the saddle from the pre-loadedunlocked state to the locked state after attaching the implanted screw.The method further has the step of unlocking the locked tulip assemblyby moving the saddle from the locked state to the pre-loaded unlockedstate. The step of unlocking is accomplished by engaging threads of thesaddle with the threaded end of the tool and rotationally pulling thesaddle proximally relative to the tulip.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 is a perspective view of the tulip assembly positioned above anexemplary bone screw.

FIG. 2 is an explode perspective view of the tulip and saddle of thepresent invention above an exemplary bone screw.

FIG. 3 is a perspective view of the tulip assembly shown attached to theexemplary bone screw.

FIG. 4 is a cross-sectional view of the tulip assembly in a pre-loadedunlocked state with the saddle shown attached onto the head of anexemplary bone screw.

FIG. 5 is a cross-sectional view showing the tulip assembly wherein aninternal saddle has been moved to the locked position or state.

FIG. 6 is a plan view of a tool end with a threaded end for attaching tointernal threads of the saddle.

FIG. 7 is a cross-sectional view taken from FIG. 6 showing the tool endthreaded into the saddle with the saddle having been moved relative tothe tulip into the locked state.

FIG. 8 is a perspective view of the tool end above the tulip assemblyand bone screw illustrating removal of the tool after locking oralternatively showing how the tool can be used to unlock the saddle toallow the tulip assembly to be removed from an implanted bone screw.

FIG. 9 shows the tulip assembly attached to the tool for eitherattachment to the exemplary bone screw or alternatively after removalfrom the bone screw.

FIG. 10 shows in cross-section the tulip assembly and unlocked saddleattached to the tool for attachment to or alternatively as occurs onremoval from said bone screw.

FIG. 11 is a cross-sectional view illustrating the tulip assembly withthe saddle in a preloaded unlocked state over an exemplary bone screw.

FIG. 12 is a cross-sectional view showing the tulip assembly wherein theinternal saddle has been moved to the locked position or state and anexemplary fixation rod is being held in the proximal end of the saddlesecurely fixed by the exemplary set screw threadingly engaged in theinternal threads of the two opposing walls of the tulip.

FIG. 13 is a perspective view of the tulip of the present invention.

FIG. 14 is a cross-sectional plan view of the tulip taken from FIG. 13.

FIG. 15 is a perspective view of the saddle of the present invention.

FIG. 16 is a plan view of the saddle taken from FIG. 15.

FIG. 17 is a cross-sectional view illustrating an alternative embodimentof the present invention tulip assembly with the saddle in a preloadedunlocked state over an exemplary bone screw.

FIG. 18 is a cross-sectional view of the alternative embodiment showingthe tulip assembly wherein the internal saddle has been moved to thelocked position or state and an exemplary fixation rod is being held inthe proximal end of the saddle securely fixed by the exemplary set screwthreadingly engaged in the internal threads of the two opposing walls ofthe tulip.

FIG. 19 is a plan view of the alternative tulip of the presentinvention.

FIG. 20 is a cross-sectional plan view of the tulip taken from FIG. 19.

FIG. 21 is a perspective view of the alternative embodiment saddle ofthe present invention.

FIG. 22 is a cross-sectional view of the saddle taken from FIG. 21.

FIG. 23 is a cross-sectional view of a tool used to unlock a screw froma tulip.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, a perspective view of the modular tulipassembly 10 of the present invention is shown. As shown, the modulartulip assembly 10 has a rod receiving tulip 20, and internal of the rodreceiving tulip 20 is shown a saddle 40, the saddle 40 is interlockinglyheld inside a distal portion of the tulip 20. Below the tulip assembly10, is shown an exemplary bone screw 2. The bone screw 2 has a threadedshank 4 for engaging bone and a rounded spherical or hemispherical head6 at the proximal end of the shank 4. This head 6 is configured toprovide polyaxial movement of the bone screw 2 relative to the tulipassembly 10 on assembly. This polyaxial movement is maintained as longas the tulip assembly 10 is not locked into position and fixed.

The modular tulip assembly 10 is basically a two part device with thetulip 20 and the preloaded saddle 40 for use with a bone screw 2. Thebone screw 2 can be preloaded into the assembly 10 to make a threecomponent device or system if desired. An important feature of thepresent invention is a binary locking aspect where a single lockingprojection 25 in combination with a groove or recess 42 holds the saddle40 in a preloaded state inside the modular tulip 20 and when the modulartulip assembly 10 is moved onto the head 6 of a bone screw 2 the saddle40 can be moved into a locked state and, if desired, can be unlocked ina reversible fashion making the modular tulip assembly 10 mostconvenient to use. These features are fully described in detail asfollows.

With reference to FIG. 2, the modular tulip assembly 10 is shown in anexploded view with the saddle 40 shown below and between the tulip 20and the bone screw 2.

In FIG. 3, the tulip assembly 10 is shown attached to the exemplary bonescrew 2 in a perspective view. The tulip 20 is fully separatelyillustrated in FIGS. 13 and 14.

With reference to FIG. 4, a cross-sectional view of the tulip assembly10 is shown wherein the saddle 40 is positioned over the polyaxialhemispherical head 6 of the exemplary bone screw 2. As shown incross-section, the tulip 20 is shown with opposing walls 22, 23 withinternal threads 24 defining a rod receiving slot or channel 33. Belowthe internal threads 24 is illustrated the saddle 40. The saddle has alocking groove or recess 42 affixed to a locking projection 25 in thetulip 20 of the tulip assembly 10. As further shown, and with referenceto FIGS. 15 and 16, the saddle 40 has a proximal end 44 with a rodreceiving concavity 45 that is aligned with the channel 33 of the tulip20. At the proximal end 44 of the saddle 40 there is a central opening41 that is threaded with threads 43, as illustrated. The locking grooveor recess 42 is shown near the proximal end 44 of the saddle 40. Belowthe locking groove or recess 42 is shown a plurality of axiallyextending flexible fingers 52 that are spaced apart by slots or slits54. At a distal end 51, these arcuate curved flexible fingers 52 arebowed slightly inwardly. At the proximal end of the slot 54 is anenlarged circular hole 55 to provide stress relief and also increase theflexibility of the fingers 52. This is important in that the fingers 52must flex or bow outwardly in order to expand as they slide over thehemispherical head 6 of the exemplary bone screw 2. As shown in FIG. 4,the plurality of arcuate fingers 52 extend downward past the maximumdiameter (d max) of the polyaxial hemispherical bone screw head 6. Thefingers 52 extension creates at least a hemispherical concavity 53 thatextends beyond the maximum diameter d max and as such, the curvature ofthe fingers 52 bends outwardly at the proximal end and bows inwardlytowards the distal end 51, however, when attached to the bone screw 2,all of the fingers 52 are shown deflected outwardly. As shown in FIG. 4and also in FIG. 14, in cross-section, the tulip 20 has a large internalchamber 30 above the distal end 31. This chamber 30 is configured toallow the fingers 52 of the saddle 40 to bow outwardly on assembly. Oncethe fingers 52 have bowed or flexed outwardly to pass the maximumdiameter d max of the bone screw head 6, they will conform or flex backinwardly compressing and sliding against the surface 8 of thehemispherical bone screw head 6. Preferably, the concavity 53 formed bythe plurality of arcuate fingers 52 is sized to complimentarily fit thehead 6 of the bone screw 2 to which it is to be attached.

With reference to the proximal end 44 of the saddle 40, as shown, theproximal end 44 is shown above where the grove or recess 42 ispositioned over a projection 25 in the tulip 20. The outer or exteriorsurface of the proximal end 44 has a small rounded edge or chamfer 48 tofacilitate sliding over the projection 25. When the saddle 40 isoriented in this position, it is in a preloaded and unlocked positionwherein the arcuate extended fingers 52 are allowed to move inwardly andoutwardly relative to an axis of the tulip 20. with reference to FIG. 5,the saddle 40 is shown moved in a locking position wherein the proximalend 44 of the saddle 40 is moved past the locking projection 25 of thetulip 20 and the groove or recess 42 is moved from the lockingprojection 25 and the proximal end 44 of the saddle 40 is move pastabutting the locking projection 25. In this state, the saddle 40 isprevented from any proximal movement relative to the tulip 20 and thearcuate fingers 52 have been pressed into the distal opening 32 of thetulip 20 between the head 6 of the polyaxial screw 2 and the distal end31 of the tulip 20. This causes the arcuate fingers 52 to be flexedinwardly, tightly grasping against the polyaxial head 6 of the bonescrew 2. This assembly can be accomplished when the bone screw 2 isimplanted in bone. In such a case, the modular tulip assembly 10 withthe saddle 40 in the unlocked position can be positioned over the head 6of the bone screw 2, pushed onto the bone screw 2 and thereafter thesaddle 40 moved into the locking position.

With reference to FIGS. 6-10, the tulip assembly 10 is shown attached tothe bone screw 2 with the assistance of a tool 100. The tip 102 of thetool 100, illustrated in FIG. 6, has a threaded end 103, alsoillustrated in FIG. 7 in a cross-sectional view, that is engaged withthe internal threads 43 of the saddle 40. The end 102 of this tool 100is configured to threadingly engage the saddle 40 and in so doingenables the tool 100 to push against the saddle 40, the outer shoulder106 of the tool 100 is adapted and precisely dimensioned to abut aproximal end 27 of the tulip 20 along the opposing walls 22, 23. Whenthis occurs and the internal shaft 101 of the tool 100 is rotated, itwill push the saddle 40 directly axially distally moving the saddle 40from the preloaded unlocked position to the locked position asillustrated in FIG. 7. FIG. 8 shows the tool 100 separated from thetulip assembly 10 as the tool 100 is being removed after the assembly isaccomplished or FIG. 8 can be viewed alternatively as a removal tool 100assisted illustration wherein the tulip assembly 10 when attached andlocked onto an implanted bone screw 2 can be physically removed bythreading the end 103 of the tool 100 into the internal threads 43 ofthe saddle 40 and rotating in such a fashion that is pulls the saddle 40in the proximal direction relative to the tulip 20. When this occurs,the saddle 40 will move from the locked position as the fingers 52 willbe released from the distal end 51 and moved upward into the chamber 30within the tulip 20 as the groove or recess 42 is positioned onto thelocking projection 25, when this occurs, the tool 100 can be used topull the tulip 20 with unlocked saddle 40 away from the implanted bonescrew 2, as illustrated in FIG. 9. It is understood while the bone screwis shown not embedded in bone just for simplification, it is to beappreciated that this procedure can be accomplished while the bone screw2 is implanted in a vertebral body. The cross-sectional view of FIG. 10illustrates how the fingers 52 are allowed to flex when the bone screw 2has been removed and a saddle 40 is prepositioned in the unlocked state.

FIG. 11 shows the tool 100 being removed from the tulip assembly 10.

With reference to FIG. 12, once the assembly is made, it is possible toplace a spinal fixation rod 60 into the concavity at the proximal end 44of the saddle 40. Once the rod 60 is in position, a threaded set screw80 can be driven down into the internal threads 24 of the opposing walls22, 23 of the tulip 20. The set screw 80 will then lock the rod 60 intoposition. When this occurs, the entire assembly is locked into a lockedposition.

While the embodiment shown shows a single projection 25 is used for thelocked position, and a movement of the saddle 40 from an unlockedinitial state with the groove or recess 42 on the projection 25 to alocked position when in use, it is understood that a resistance or forcerequired to move the saddle 40 into the preloaded unlocked position forassembly can be adjusted depending on the amount of interference that isprovided between the projection 25 and the groove or recess 42 and theexterior surface of the proximal end 44 of the saddle 40. It is believedto have sufficient locking strength, it is preferable that the exemplarytool 100 be used so that the forces required to overcome the initialunlocked state where the recess 42 is positioned over the projection 25are such that a tool 100 is preferred. The tool 100 designed provides aforce between the tulip 20 and the saddle 40, but provides no lifting orpulling forces against the bone screw 2 which can be embedded in bone.This is important in that one does not want to loosen a bone screw 2that has been attached into a vertebral body, but rather would like theforces for locking the saddle 40 in positon relative to the tulip 20 beabsorbed between the tool 100, the tulip 20 and the saddle 40 withoutany particular axially loads pulling or loosening the bone screw 2.

With reference to FIG. 17, a cross-sectional view of the modular tulipassembly 10A of the present invention is shown. As shown, the modulartulip assembly 10A has a rod receiving tulip 20A, and internal of therod receiving tulip 20A is shown a saddle 40A, the saddle 40A isinterlockingly held inside a distal portion of the tulip 20A. Below thetulip assembly 10A, is shown an exemplary bone screw 2. The bone screw 2has a threaded shank 4 for engaging bone and a rounded spherical orhemispherical head 6 at the proximal end of the shank 4. This head 6 isconfigured to provide polyaxial movement of the bone screw 2 relative tothe tulip assembly 10A on assembly. This polyaxial movement ismaintained as long as the tulip assembly 10A is not locked into positionand fixed.

The modular tulip assembly 10A is basically a two part device with thetulip 20A and the preloaded saddle 40A for use with a bone screw 2. Thebone screw 2 can be preloaded into the assembly 10A to make a threecomponent device or system if desired. An important feature of thepresent invention is a binary locking aspect where a single lockingprojection 49 in combination with a proximal tulip groove or recess 21holds the saddle 40A in a preloaded state inside the modular tulip 20Aand when the modular tulip assembly 10A is moved onto the head 6 of abone screw 2 the saddle 40A can be moved into a locked state and, ifdesired, can be unlocked in a reversible fashion making the modulartulip assembly 10A most convenient to use. These features are fullydescribed in detail as follows.

With reference to FIG. 17, a cross-sectional view of the tulip assembly10A is shown wherein the saddle 40A is positioned over the polyaxialhemispherical head 6 of the exemplary bone screw 2 in an unlockedposition. As shown in cross-section, the tulip 20A is shown withopposing walls 22, 23 with internal threads 24 defining a rod receivingslot or channel 33. Below the internal threads 24 is illustrated thesaddle 40A. The saddle 40A has a locking projection 49 affixed to atulip proximal groove or recess 21 in the tulip 20A of the tulipassembly 10A. The locking projection 49 is shown near the proximal end44 of the saddle 40A. Below the locking projection 49 is shown aplurality of axially extending flexible fingers 52 that are spaced apartby slots or slits 54. At a distal end 51, these arcuate curved flexiblefingers 52 are bowed slightly inwardly. At the proximal end of the slot54 is an enlarged circular hole 55 to provide stress relief and alsoincrease the flexibility of the fingers 52. This is important in thatthe fingers 52 must flex or bow outwardly in order to expand as theyslide over the hemispherical head 6 of the exemplary bone screw 2. Asshown in FIG. 17, the plurality of arcuate fingers 52 extend downwardpast the maximum diameter (d max) of the polyaxial hemispherical bonescrew head 6. The fingers 52 extension creates at least a hemisphericalconcavity 53 that extends beyond the maximum diameter d max and as such,the curvature of the fingers 52 bends outwardly at the proximal end andbows inwardly towards the distal end 51, however, when attached to thebone screw 2, all of the fingers 52 are shown deflected outwardly. Thetulip 20A has a large internal chamber 30 above the distal end 31. Thischamber 30 is configured to allow the fingers 52 of the saddle 40A tobow outwardly on assembly. Once the fingers 52 have bowed or flexedoutwardly to pass the maximum diameter d max of the bone screw head 6,they will conform or flex back inwardly compressing and sliding againstthe surface 8 of the hemispherical bone screw head 6 when in the lockedposition illustrated in FIG. 18. Preferably, the concavity 53 formed bythe plurality of arcuate fingers 52 is sized to complimentarily fit thehead 6 of the bone screw 2 to which it is to be attached.

With reference to the proximal end 44 of the saddle 40A, as shown, theproximal end 44 is shown above where the projection 49 is positioned ina groove or recess 21, 21L in the tulip 20A. The outer or exteriorsurface of the proximal end 44 has a small rounded edge or chamfer 48 tofacilitate sliding past the tulip grooves or recesses 21, 21L. When thesaddle 40A is oriented in a preloaded and unlocked position, as shown inFIG. 17, the arcuate extended fingers 52 are allowed to move inwardlyand outwardly relative to an axis of the tulip 20. With reference toFIG. 18, the saddle 40A is shown moved in a locking position wherein thelocking projection 49 of the saddle 40A is moved past the proximalgroove or recess 21 of the tulip 20A and into the distal tulip lockinggroove or recess 21L. In this state, the saddle 40A is prevented fromany proximal movement relative to the tulip 20A and the arcuate fingers52 have been pressed into the distal opening 32 of the tulip 20A betweenthe head 6 of the polyaxial screw 2 and the distal end 31 of the tulip20A. This causes the arcuate fingers 52 to be flexed inwardly, tightlygrasping against the polyaxial head 6 of the bone screw 2. This assemblycan be accomplished when the bone screw 2 is implanted in bone. In sucha case, the modular tulip assembly 10A with the saddle 40A in theunlocked position can be positioned over the head 6 of the bone screw 2,pushed onto the bone screw 2 and thereafter the saddle 40A moved intothe locking position.

With reference to FIGS. 17-23, the alternative embodiment tulip assembly10A is shown attached to the bone screw 2 with the assistance of a tool100. The tip 102 of the tool 100, illustrated in FIG. 23, has a threadedend 103 that is engaged with the internal threads 43 of the saddle 40A.The end 102 of this tool 100 is configured to threadingly engage thesaddle 40A and in so doing enables the tool 100 to push against thesaddle 40A, the outer shoulder 106 of the tool 100 is adapted andprecisely dimensioned to abut a proximal end 27 of the tulip 20A alongthe opposing walls 22, 23. When this occurs and the internal shaft 101of the tool 100 is rotated, it will push the saddle 40A directly axiallydistally moving the saddle 40A from the preloaded unlocked position ofFIG. 17 to the locked position as illustrated in FIG. 18. FIG. 23 showsthe tool 100 inserted in the tulip assembly 10A as the tool 100 is beingremoved after the assembly is accomplished or FIG. 23 can be viewedalternatively as a removal tool 100 assisted illustration wherein thetulip assembly 10A when attached and locked onto an implanted bone screw2 can be physically removed by threading the end 103 of the tool 100into the internal threads 43 of the saddle 40A and rotating in such afashion that is pulls the saddle 40A in the proximal direction relativeto the tulip 20A. When this occurs, the saddle 40A will move from thelocked position as the fingers 52 will be released from the distal end51 and moved upward into the chamber 30 within the tulip 20A as thelocking projection 49 is positioned into the proximal tulip lockinggroove or recess 21, when this occurs, the tool 100 can be used to pullthe tulip 20A with unlocked saddle 40A away from the implanted bonescrew 2. It is understood while the bone screw is shown not embedded inbone just for simplification, it is to be appreciated that thisprocedure can be accomplished while the bone screw 2 is implanted in avertebral body. The cross-sectional view of FIG. 17 illustrates how thefingers 52 are allowed to flex when the bone screw 2 is not locked andsaddle 40A is prepositioned in the unlocked state.

These and other objectives are achieved by the application of thepresent invention as described above.

Variations in the present invention are possible in light of thedescription of it provided herein. While certain representativeembodiments and details have been shown for the purpose of illustratingthe subject invention, it will be apparent to those skilled in this artthat various changes and modifications can be made therein withoutdeparting from the scope of the subject invention. It is, therefore, tobe understood that changes can be made in the particular embodimentsdescribed, which will be within the full intended scope of the inventionas defined by the following appended claims.

1.-12. (canceled)
 13. A method of assembling a tulip comprises the stepof: providing a tulip with a pair of grooves or recesses, the pair ofgrooves or recesses being a proximal groove or recess and a distallocking groove or recess; and positioning a saddle with a concavelocking surface inside the tulip into a proximal groove or recess insidethe tulip in a pre-loaded unlocked state to receive a head of a bonescrew.
 14. The method of claim 13 further comprises the step of: pushingthe tulip with the pre-loaded unlocked saddle onto an implanted bonescrew previously threaded into bone.
 15. The method of claim 14 furthercomprises the step of: moving the saddle to a locked state by moving thelocking projection from the proximal tulip groove or recess distallyinto the distal tulip locking groove or recess.
 16. The method of claim15 of moving the saddle to a locked position further includes engaginginternal threads of the saddle with a threaded end of a tool, rotatingthe tool to move the saddle from the pre-loaded unlocked state to thelocked state after attaching the implanted screw.
 17. The method ofclaim 16 further comprises the step of: unlocking the locked tulipassembly by moving the saddle by moving the saddle from the locked stateto the pre-loaded unlocked state.
 18. The method of claim 17 wherein thestep of unlocking the tulip assembly includes engaging threads of thesaddle with the threaded end of the tool and rotationally pulling thesaddle proximally relative to the tulip. 19.-30. (canceled)